Forward scatter optical turbidimeter apparatus

ABSTRACT

An optical turbidimeter including a light source for generating a ribbon-shaped light beam for transmission through a fluid process stream, a first light detector for measuring the intensity of the light beam after passage through the process stream, a second light detector responsive to light scattered in the forward direction by the direct beam, spatial filtering optics for focusing the scattered light only from a center section of the direct beam onto the second detector and electronic signal processing means responsive to the signals generated by the two detectors for developing an output signal proportional to the ratio of the scattered light to the transmitted light beam.

United States Patent Simms 1 Jan. 30,1973

541 FORWARD SCATTER OPTICAL 3,506,360 4 1970 Albert ..356/104 xTURBIDIMETER APPARATUS 3,518,437 6/1970 Riggs ..356/207 x FOREIGNPATENTS OR APPLICATIONS Primary Examiner-Ronald L. Wibert AssistantExaminerF. L. Evans Attorney-Lowhurst & Hamrick [57] ABSTRACT An opticalturbidimeter including a light source for generating a ribbon-shapedlight beam for transmission through a fluid process stream, a firstlight detector for measuring the intensity of the light beam afterpassage through the process stream, a second light detector responsiveto light scattered in the forward direction by the direct beam, spatialfiltering optics for focusing the scattered light only from a centersection of the direct beam onto the second detector and electronicsignal processing means responsive to the signals generated by the twodetectors for developing an output signal proportional to the ratio ofthe scattered light to the transmitted light beam.

[75] Inventor: R. John Simms, Menlo Park, Calif.

[73] Assignee: Agricultural Control Systems,

Redwood City, Calif.

[22] Filed: Nov. 25, 1970 211 Appl. No.1 92,707

[52] US. Cl. ..356/208, 250/218, 356/104 [51] InLCl. ..G0ln 21/26 [58]Field of Search ..356/36, 37, l02104, 356/207-208; 250/218 [56]References Cited UNITED STATES PATENTS 3,310,680 3/1967 Hasegawa..356/104 3,535,531 10/1970 Neitzel ....250/2l8 X 3,576,558 4/1971Devries.... ....356/104 X 3,340,764 9/1967 Bergson ..356/l77 3,409,88511/1968 Hall ....356/104 X 3,528,743 9/1970 Scott et al. ..356/1043,203,309 8/1965 Skala et a1 ..356/37 3,361,030 1/1968 Goldberg.......250/218 X 3,431,423 3/1969 Keller ..250/218 [2 i| 1 I1 I v LIGHT 261 57 32 3 SOURCE 7 17S:

30 44 (gEAM I6 HAPlNG DETECTOR 2/1938 Great Britain ..356/l04PATENTEDJAH 30 1975 TURBIDITY (ARBIT UNITS) F. S.

AMPLITUDE 3. 71 3. 743 SHEET 2 F 2 TURBIDITY UNITS vs NEPHELOS UNITS ITo f/ 60 O g 1 l IO I5 NEPHELOS 2C.)

TIME

F /'g 5 Z2 78 80 {84 F TER CONTROL TURBDIMETER APPARATUS FILTER AID TANK88 FLOW A STREAM OUTPUT 90 PRECOAT INVENTOR TANK R. JOHN SIMMS BY F .6W? W INPUT ATTORNEYS.

' FORWARD SCATTER OPTICAL TURBIDIMETER APPARATUS BACKGROUND OF THEINVENTION The present invention relates generally to instrumentation formeasuring the turbidity of a fluid and more particularly to a noveloptical turbidimeter utilizing forward scatter principles to accuratelyprovide turbidity data.

Among the prior art which may be of interest, are the US. Pat. Nos. toSinclair 2,812,686, Keim et al 3,281,602, Muta et al 3,279,305, Hach3,309,956, Ewing 3,364,812, Keller 3,431,423 and Albert 3,506,360.

Turbidity is the name given to one of the optical properties of a liquidand is related to the presence, nature and the amount of discreteaggregations of material different from the pure liquid carrier.Turbidity is usually observed as the degradation in the contrast of animage transmitted through the liquid (for example the Jackson candletechnique) or as the percentage of light emerging from the sample atangles different from the direct transmitted direction (forward,perpendicular or back scattered detection). The physical phenomenacontributing to the observed turbidity are absorption, specular anddiffuse, surface scattering and diffraction by particles and bubbles.The relative contributions of each phenomenon depend strongly upon thephysical and optical characteristics of the particles and the hostmedium and on the details of the observation technique.

In using a turbidity measurement to control or predict the opticalappearance of the sample without attempting to deduce the nature orconcentration of the scatterers it is only necessary to insure that theinstrumental technique reproduces the conditions under which the productwill be judged. For example, swimming pool water is likely to be faultedfor poor image transmission, whereas a glassof beverage will probably bejudged by narrow angle forward scattering from a distant source.

The direct measurement of transmission for turbidity determination isgenerally too low in precision and is affected by too many extraneousfactors to be of any value except for high levels of turbidity. theusual techniques for turbidity measurement rely on the phenomena of backscattering, perpendicular scattering (Nephelometry) or forwardscattering. Each of these techniques is differently affected by thephysical and optical properties of the particles in question and it isnot feasible in a general situation to expect correlation between theresults obtained by using different techniques.

Two working units of turbidity have found some acceptance. These are thescale of Jackson turbidity units (JTUs) based on the Jackson candletechnique and parts per million of equivalent diatomaceous earth. Theformer is a purely optical scale and correlates fairly well with forwardscattering measurements no conclusion is drawn concerning the nature andconcentration of the scattering particles. The latter scale attempts toperform this correlation and is therefore suspect. However, therequirements of production related turbidity problems have led to itswidespread use.

When the measurement goal is optical in nature, the JTU scale iseffective and forward scattering techniques are suitable for the relatedinstrumentation. Most subjective turbidity judgments are made underthese conditions since the scattering effects are often several ordersof magnitude larger in intensity than for perpendicular or backscattering effects. However, the difficulty of designing reliableforward scatter instruments which are not affected by stray light orunwanted scattering sources has heretofore prevented the technique fromachieving the widespread use required for credible utilization ofturbidity measurements in quality control.

SUMMARY OF THE INVENTION ln accordance with a preferred embodiment ofthe invention, a narrow, ribbon-shaped beam of light is passed throughthe fluid of which the turbidity is to be measured and is received by afirst or transmitted beam detector which provides a first output signalcommensurate with the light content of the transmitted beam. Thethickness of the beam of light is selected as thin as practicallypossible, in the direction of fluid flow, taking into account suchfactors as desired light output and practical beam shaping means, toallow for best bubble rejection. Further, spatial filtering means isprovided which receives the light which is forward scattered by thetransmitted beam and which passes only the light scattered by a selectedportion of the center section of the transmitted beam to a second orscattered light detector which provides a second output signalcommensurate with the light content of the forward scattered light ofthe selected center portion of the beam. The ratio of the two outputsignals is then developed and provides a measure of the fluid turbidi-It is therefore a principal object of the present invention to providean optical turbidimeter apparatus for determining the turbidity of afluid by spatially filtering the forward scattered light from a lightbeam passed through the fluid to eliminate the effects of observationwindow scattering and of other unwanted sources of scattered andreflected light.

Another object of the present invention is to provide an opticalturbidimeter apparatus for measuring turbidity of a fluid process streamwherein the forward scattering of a sharply defined narrow beam oflight, directed through the process stream, is detected separate fromthe directly transmitted beam of light to develop a ratio output signalwhich is proportional to turbidity and is independent of sample colorand refractive index.

Still another object of the present invention is to provide an opticalturbidimeter apparatus for measuring the turbidity of a fluid processstream which includes means for passing a sharply defined beam oflightwhich is rectangular in transverse cross section through the processstream, means for detecting both the directly transmitted beam of lightand the forward scattered light from a selected portion of the lightbeam and means for providing an output signal proportional to the ratioof the scattered light to the directly transmitted light and which isindependent of sample color and refractive index.

Still another object of the present invention is to provide an opticalturbidimeter apparatus for measuring the turbidity of a fluid processstream which includes means for passing a sharply defined beam of light,which has as small a dimension as possible in the direction of flow ofthe process stream, means for detecting both the directly transmittedlight and the light scattered in the forward direction from a selectedportion of the process stream, means for providing an output signalproportional to the ratio of the scattered light to the directlytransmitted light, and means to filter the output signal to removetherefrom the spikes caused by bubbles.

Other objects of the present invention will become apparent to thoseskilled in the art after having read the following detailed descriptionof the preferred embodiment which is illustrated in the several figuresof the drawing.

IN THE DRAWING FIG. 1 is a cross section taken through a generalizedembodiment of the turbidimeter of the present invention.

FIG. 2 is a detail illustrating the shape of the light beam passedthrough the flow stream in accordance with the present invention.

FIG. 3 is a chart showing correlation between Nephelos UnitsandTurbidity Units obtained in accordance with the present invention.

FIG. 4 is a graph illustrating turbidimeter output and showingsuperimposed spikes caused by the presence of bubbles in process stream.

FIG. 5 is a schematic diagram of an electronic integrator circuitutilized to reject bubble responsive spikes in the output signal fromthe direct beam detector.

FIG. 6 illustrates in diagram form a fluid processing system in whichthe present invention is utilized to monitor the turbidity of theprocess stream.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1of the drawing, there is shown a preferred embodiment of theturbidimeter apparatus of the present invention suitable for use incontinuously monitoring the turbidity of a fluid process stream. Theapparatus includes a short flanged section of conduit 10 which can bebolted to the end flanges of the conduits 12 and 14 for in-linemonitoring applications. Provided in opposite walls of the section 10are sight glass windows 16 and 18. A light source housing 20 is affixedto section 10 adjacent sight glass window 16, and a light receiverhousing 22 is mounted to section 10 about sight glass window 18.Included within housing 20 is a source of light 24 which is preferably alaser, but may alternatively be comprised of an incandescent filamentlamp or other source of visible, ultraviolet or infrared radiation forgenerating a beam of light 26.

Positioned between light source 24 and window 16 are special beamshaping optics 28 which convert light beam 26 into a thin ribbon-shapedbeam of light 30 which is transmitted along an optical axis 32 passingthrough entrance window 16, the process stream 34 and exit window 18.The ribbon-shaped configuration of light beam 30 is illustrated in FIG.2 of the drawing. For reasons explained hereinafter in connection withbubble rejection, the ribbon thickness, in a direction parallel to fluidflow, is made as thin as practically possible, and normally but notnecessarily occupies at least 50 percent of the cross-sectional area ofthe stream 16. For bubble rejection,,a thickness of less than 5mm. isdesirable and about 2mm. has produced good average measurement ofturbidity of the stream.

Positioned within the receiver housing 22 and spaced, in that orderalong the optical axis 32, is a first or direct beam light detector 36,an imaging lens system 38, a second or scattered light detector 40 and amasking element 42 dispose and covering the light sensitive face ofdetector 40. Detector 36 is a strip detector for receiving only thetransmitted light beam 30 which passes through process stream 34.Imaging lens system 38, detector 40 and mask 42 in combination provide afield defining spatial filtering system which focuses light scatteredfrom a particular portion 44 of light beam 30 onto the light sensitiveface of detector '40. Whereas the outer periphery of the light sensitiveface of detector 40 cooperates with system 38 to define the rearmostedge 43 of light beam portion 44, masking element 42 cooperates with thesystem 38 to define the foremost edge 45 of light beam portion 44 bypreventing scattered light eminating from any portion of light beam 30other than portion 44 from reading the scattered light detector. Thespatial filtering system thereby further insures that no scattered lightfrom the entrant and exit window surfaces reaches second detector 40.

The positions and sizes of the masking element 42 and detector 40 may berearranged with respect to the focal plane of system 38 to eitherlengthen, shorten or change the extremities of portion 44. Thisinvention is not intended to be limited to the particular embodimentillustrated, but includes all such systems wherein the size and positionof lenses, masking element and detectors define the regions along theoptical axis from which scattered light is accepted by the detectors ordefine regions from which scattered light cannot reach the detectors.

The output signals generated by detectors 36 and 40 are coupled by leads46 and 48, respectively, to a suitable signal processor 50 wherein thetwo signals are amplified, detected and demodulated, if necessary, andwherein their ratio is computed. The resultant ratio output signal maybe used to drive a recorder 52. which provides a permanent record of theturbidity of the process stream. The ratio computation results in asignal which is independent of source fluctuations, line voltagevariations and other environmental factors which would otherwise affectthe calibration stability. The synchronous demodulation, if employed, ofboth signals further increases the long term stability and provides. ahigh degree of noise immunity, yet enables the system to respond with atime constant on the order of 0.1 seconds.

In the preferred embodiment, a calibration shutter 54 and reflectors 55and 57 may also be provided within light source housing 20 so as topermit accurate calibration of the apparatus. Calibration isaccomplished by depressing a push button at a control panel control ofsignal processor 50 is then adjusted to provide a corresponding increasein the output of recorder 52 or other associated readout meters. This istypically a second operation and need only be performed at infrequentintervals.

The turbidimeter apparatus of the present invention, since unaffected bystray light or unwanted scattering sources, makes for creditableutilization of turbidity measurements in quality control operations andthe operator can now be certain that his turbidity measurementscorrelate well with the JTU scale and with optical phenomenon observedby the consumer of the product in question. By way of comparison, the 90and back scatter techniques of the prior art do not exhibit thiscorrelation and thus make forward scatter instruments preferable forthese types of measurements.

Although the optically consistent JTU scale does not by itself indicatethe nature of concentration of the scattering particles, the scatteringsignals from a specific type of particle in a single medium will, in thelow turbidity range, be proportional to particle concentration. This isall that is required in a situation such as the monitoring of aproduction process, e.g., filtration, and is the basis of the parts permillion equivalent diatomaceous earth scale. The turbidity readings fora single product type, after a uniform treatment process, can normallybe mutually correlated, thus providing the necessary production control,but the readings usually will not correlate with those for a differentmedium or for different sizes and types of scattering particles. Forexample, the curve of turbidity vs. ppm. rust particles in water willenable the concentration of these rust particles to be controlled butwill be different from the calibration curve for rust particles ofconsiderably different sizes for clay particles and for asbestosparticles. These limits are inherent in the basic interaction of lightwith matter and cannot be circumvented by an optical scatteringmeasurement alone. However, as long as those limitations are understood,the measurement of turbidity by the forward scattering technique isideal for the monitoring of specific operations such as filtration,settling or coagulating efficiency and will provide the necessary datafor determining the optical turbidity or clarity of the outgoingproduct. Conversely, the comparison of turbidity measurements betweendifferent laboratories, plants or industries will indicate the correctdegree of correlation between the optical variable of turbidity (inJTUs) or its relative equivalent in ppm. diatomaceous earth, but willnot necessarily reveal information on the nature or concentration of thescattering particles.

Aseries of extended experiments was conducted to establish thecorrelation between data obtained from the turbidimeter of the presentinvention, using forward scattering principles, and Nephelos readingsobtained from a standard laboratory Nephelometer utilizing perpendicularscattered light. The samples were beer, varying degrees of filterprocessing and with different intensities of chill haze. The suspendedmatter generating the scattered signals was a mixture of proteinagglomerations (causing the chill haze), diatomaceous earth andfilterable organic particulates. The sample temperature at theturbidimeter was 2C and since the chill haze contribution wassignificant, the sample temperature for the Nephelometer readings had tobe held at 2C. The design of the Nephelometer necessarily results in anuncertain sample temperature and this factor represents the greatestsource of error in the experiments. In practice, the Nephelometersamples were between 2C and 4C for the measurements. However, a 2Cdifference in sample temperature resulted in a 1 unit change inNephelometer reading. The uncertainty in turbidity reading is equivalentto i 0.1 Nephelos Units. As shown in the results illustrated in FIG. 3of the drawing, the correlation holds over the range studied within theexperimental error of the Nephelometer.

The conclusion to be drawn from this data is that for the type of sampleand the scattering particulates of this study the turbidimeter of thepresent invention can be directly calibrated in Nephelos, or some other90 scattering unit, and can be operated for process control purposeswith standards and limits based on 90 scattering techniques. This degreeof correlation between data obtained from the two instrumentaltechniques is expected for any group of samples of a single type ofscatter in a single medium. However, when different types of scatteringparticles are encountered, the mu- .tual correlation is expected todecrease. As pointed out above, the turbidimeter data is expected tofollow the ppm. concentration of the scatter more closely than the datafrom a 90 system.

A typical output curve of the type obtained from the preferredembodiment of the turbidimeter is illustrated in FIG. 4 of the drawing.The curve 60 illustrates the generally slowly varying and occasionallyspiked DC output, representing the ratio of the first and second outputsignals as provided by processor 50, responsive to the turbidity of thefluid process stream. The single spike 62 and the multiple spikes 64 aretypically the results of bubbles appearing in the process stream. Aslong as the ribbon of light crossing the process stream is narrow, sayabout 2 millimeters thick in the direction of the stream flow, bubblesin the stream cause short spurious signal spikes or pulses 62 and 64superimposed on the otherwise steady turbidity signal. These spikes,which are primarily in the scattered beam signal, can be filtered, if sodesired, by the addition of a simple electrical filter circuit. In thecase of a thick ribbon of light, the number of bubbles is of course muchgreater and the effect of such bubbles is a wide pulse, like acontinuum, which is very difficult to filter. Accordingly, bubblerejection requires a very thin ribbon of light so that bubbles cause asharp spike disturbance which can readily be filtered.

One such filter circuit is illustrated in simplified form in FIG. 5 andis used preferably to couple processor 50 to recorder 52. Circuitincludes a first amplifier 72 which amplifies the processor outputsignal and feeds it through an integrator, comprised of a resistor 74and capacitor 76, and through a second amplifier 78. A diode is shuntedacross resistor 74 and is back biased by any positive going peaks in thedetector out put and forward biased by any negative going signalstherein. The circuit thus operates to effectively eliminate spikes inthe output which are attributed to bubbles. Such circuitry is usuallynot required in in-line systems since the normal use of bubblesencountered with sampling turbidimeters the evolution of disolved gasbubbles due to the drop from line pressure to atmospheric is usually notencountered with the inline system because the sample remains at linepressure. It should, however, be pointed out that just as the spikerejection circuit can be utilized to eliminate the effect of bubbles inthe flow stream, appropriate circuitry can likewise be used to evaluatethe size of the bubbles or other particulate matter, since the sizethereof will have a definate relationship to the parameters of thepulse-shaped signals.

The output signals from the apparatus of the present invention can beused for monitoring the efficiency of filtration operations, forinforming the operator when precoat filters are ready for use, or at theend of their life, for automatic redirection in the event of filterbreakthrough or process failure, and for part of the control operationin completely automatic filtration systems. The continuous recordproduced by the apparatus is available for identifying the highturbidity points in the process cycle for corrective action, forproduction planning and quality assurance requirements. Many of thesefunctions are not now performed, and those which are, usually rely uponsubjective judgments based on no identifiable objective critera.However, the present invention now provides the capability forestablishing all these operations on a rational, scientific andobjective basis.

The turbidimeter of the present invention is ideal for monitoring and/orcontrolling the turbidity parameter in industrial filter operations.Since the purpose of such a filter is to remove suspended material fromthe process stream, a measurement of the output turbidity is the onlydirect method of evaluating the performance of the filter. Theturbidimeter is thus used for monitoring and controlling the precoatcycle of the filter, to switch the filter on-stream when the precoatcycle is complete, to monitor for filter breakthrough, to switch theunit into recirculation in the event that breakthrough occurs, to returnto on-stream operation when the filter is rescaled, and to signal theend of the on-stream phase if this results from a deterioration inoutput turbidity. A simplified block diagram of an automaticallycontrolled system is illustrated in FIG. 6 of the drawing.

In this system, the turbidimeter 80 monitors the output of filter 82 atall times. In the event that the control apparatus 84, which isresponsive to the turbidimeter 80, senses excessive turbidity the maininput valve 86 and output valve 88 are shut off and the closed loopthrough the empty precoat tank 90 is established. The filter will thenself-heal during the recirculation and once the output turbidity hasimproved control apparatus 84 will reopen valves 86 and 88 and theonstream operation will be resumed.

If bubbles are anticipated in the filter output, it is recommended thatthe bubble rejection circuitry illustrated in FIG. be included in theturbidimeter data processing package. it is also suggested that whenlarge receiving tank volumes are used the control system includes aninstant-reset time delay responsive to the alarm signal generatedthereby. This will insure that an alarm condition must continuouslyexist for the duration of the time delay before the recirculationoperation is actuated. In this case, short periods of excessiveturbidity, which can perhaps be tolerated, do not interrupt the process.

To render the operation of such a filter system automatic, theparameters to be monitored should be turbidity, pressure drop across thefilter, flow rate and possibly a cake thickness monitor. The first threevaria- 5 bles are conducive to measurement by external transducers andthese can be retrofitted to an existing system. The last parameter isless important for the routine operation of the filter and in most casesbe included in the fabrication of the filter if pressure certificationis necessary. The three important variables are reducible to threethreshold levels with a possible interrelationship between the flow rateand the pressure differential thresholds.

The operation of the various valves is controlled by the three digitalconditions of these thresholds and the control apparatus can berelatively straight forward. However, it is not necessary to convert thefilter operation to automatic control to achieve the benefits of theturbidity monitor. Since the turbidity signal is the only measurement ofefficiency of the removal of suspended solids, a turbidity signal whichexceeds the threshold can actuate an alarm to attract the operatorsattention. During the precoat cycle, the operator is already concernedwith the turbidity. The use of the monitoring system with a meter orrecorder display will thus enable him to judge the end of the precoatingoperation by an objective bubble free measurement of the turbidity. Thepresent invention provides this means of objective measurement free of.the source of error encountered using prior art systems and is speciallydesigned for the type of application.

While the principal purpose of the invention is to provide an improvedmeans for making turbidity measurements, the apparatus is readilyadaptable for use in other applications. For example, any applicationwherein the continuous monitoring of a fluid process stream forirregularities or the specific detection of particular size particles orobjects suspended within such process stream is considered to be withinthe scope of the invention. The source of illumination in the form of alaser beam is very attractive since it requires no special shapingoptics and is very narrow, and therefore eminently suitable for bubblerejection.

The disclosure of signal conditioning electronics, which detect thepresence of spikes in the output of the light detectors, is not intendedto limit the invention to the rejection of spikes produced by thepresence of bubbles. The presence of any large particle or aggregationof particles or material which varies and is much greater in size thanthe material under examination can also be detected and their electricaleffect can be electronically rejected. Conversely, since the presence ofbubbles and large particles or aggregations of particles and materialcan also be detected by the invention, such presence can berecorded by areadout device for observation and analysis by the user.

Moreover, the apparatus is not limited to use of a thin ribbon of lightand in these applications in which bubbles form no problem, it willundoubtedly be found desirable to utilize a beam of light having athicker cross section. One of the reasons for the preferred use of beamsof rectangular cross section is the ability of the system to properlyevaluate the presence of bubbles and other particulate matter in theflow stream if the end faces are parallel to fluid flow. For example, ifa circular beam of light were utilized, a bubble or portion of a bubblemight pass through only a very small cord of the beam cross section andwould therefore not provide a meaningful indication in the output.However, where a rectangular beam is utilized, a bubble in the processstream is more likely to pass through the entire beam if it passesthrough the,beam at all, and thus more accurate data concerning thebubble can be obtained.

Neither is the present invention limited in application to measuringturbidity in the main process stream of a fluid system since it can beused with equal efficacy in a side stream or in a batch sampling system.Similarly, there is no intended limitation to use of the presentinvention in making measurements of moving sample streams since theinvention can also be used to make static fluid measurements wherein atest tube or other sample container is inserted into the path of thelight beam. In other words, chamber, as used in the claim is intended tomean any means for containing a sample fluid so that the light beam maybe passed through it.

After having read the above disclosure of a preferred embodiment, it iscontemplated that many alterations and modifications of the inventionwill become apparent to those skilled in the art. Accordingly, theinvention is not to be limited to the particular embodiments disclosed,and the appended claims are to be interpreted as covering allmodifications and applications thereof which fall within the true spiritand scope of the invention.

What is claimed is:

l. A forward scatter optical turbidimeter comprising:

a chamber for containing a liquid fluid sample the turbidity of which isto be evaluated, said chamber having opposite wall portions which areradiation transparent;

means for defining a radiation axis through said transparent wallportions;

source means disposed on one side of said chamber for developing a beamof radiation and for directing said beam of radiation across saidchamber through said wall portions along said radiation axis;

first radiation detector means disposed along said radiation axis on theother side of said chamber for receiving said beam of radiation and forgenerating a first output signal commensurate with the intensity of saidbeam of radiation after transmission through said fluid sample;

second radiation detector means disposed along said radiation axis onthe side of said first detector means opposite said chamber;

spatial radiation filtering means disposed between said first and seconddetector means, said spatial radiation filter means being arranged anddimensioned to project only the radiation scattered in the forwarddirection from a predetermined longitudinal segment of said beam ofradiation which lies wholly within said chamber and is spaced inwardlyfrom said wall portions onto said second detector means, said seconddetector means generating a second output signal commensurate with theintensity of the received forward scattered radiation; and

signal processing means responsive to said first and second outputsignals and operative to provide an indication of the turbidity of saidsample.

2. A forward scatter optical turbidimeter as recited in claim 1 whereinsaid source means includes beam shaping means for shaping said beam ofradiation into a flat ribbon which is substantially uniform along itslength.

3. A forward scatter optical turbidimeter as recited in claim 2 whereinsaid beam of radiation has a thickness of less than 5 millimeters alongthe flat portion of said ribbon.

4. A forward scatter optical turbidimeter as recited in claim 3 whereinsaid beam of radiation has a transverse width sufficient to occupy atleast 50% of the effective cross-sectional area of said chamber throughwhich said light beam passes.

5. A forward scatter optical turbidimeter as recited in claim 1 andfurther including a calibration means for permitting a predeterminedamount of light, in the form of a calibration beam, to pass through saidchamber and only onto said second detector means.

6. A forward scatter optical turbidimeter as recited in claim 1 in whichsaid spatial radiation filtering means includes, an imaging lens systemfor imaging the scattered radiation onto said second detector means, anda limiting means cooperating with said second detector means to restrictthe imaged radiation to an annulus whose inner and outer diameterscorrespond, respectively, to the near and far end portion of saidlongitudinal segment. i

7. A forward scatter optical turbidimeter as recited in claim 6 in whichsaid limiting means includes a central mask overlying said seconddetector means for defining the inner diameter of said annulus.

8. A forward scatter optical turbidimeter as recited in claim 6 in whichthe radiation sensitive portion of said second detector means extends toand defines said outer diameter of said annulus.

9. A forward scatter optical turbidimeter for monitoring the turbidityof a flowing liquid comprising:

a flow channel through which the flowing liquid is passed, said flowchannel having opposite wall portions which are optically transparent;

means for defining an optical axis through said transparent wallportions transversing said flow channel;

light source means disposed on one side of said flow channel fordeveloping and projecting a light beam, having a ribbon-like,substantially uniform cross section along its length, along said opticalaxis;

first light detector means disposed along said optical axis on the otherside of said flow channel for receiving the light from said light beamwhich is directly transmitted and for generating a first output signalcommensurate with the intensity such directly transmitted light; Y

second detector means disposed along said optical axis on the side ofsaid first detector means opposite said flow channel for receiving thelight from said light beam which is scattered in the forward directionand for generating a second output signal commensurate with theintensity of such forward scattered light; and

signal processing means responsive to said first and second outputsignals and operative to provide an indication of the turbidity of saidfluid.

10. A forward scatter optical turbidimeter as recited in claim 9 whereinsaid light source means comprises a laser and a beam expanding means fordeveloping said light beam.

11. A forward scattcr'optical turbidimeter is recited in claim 9 whichfurther includes spatial optical filtering means disposed on the side ofsaid first detector means opposite said flow channel portion, saidfiltering means being operative to project only the light scattered inthe forward direction from a predetermined longitudinal segment of saidlight beam which lies wholly within said flow channel portion and whichis spaced inwardly from said walls onto said second detector means.

12. A forward scatter optical turbidimeter as recited in claim 11wherein said spatial optical filtering means includes, an imaging lenssystem for imaging the scattered radiation on said second detectormeans, and means to limit the area of sensitivity of said seconddetector means to an annulus whose inner and outer diameters correspondto the desired end portions of said longitudinal segments. 13. A forwardscatter optical turbidimeter as recited in claim 9 which furtherincludes a calibration means for permitting a predetermined amount oflight, in the form of a calibration beam, to pass through said flowchannel and only onto said second detector means.

14. A forward scatter optical turbidimeter as recited in claim 9 whereinthe transverse cross section of said light beam is substantiallyrectangular and has a thickness in the direction of the flowing liquidwhich is less then 5 millimeters.

15. A forward scatter optical turbidimeter as recited in claim 9 whereinthe width of said light beam is suffi-' cient to occupy at least 50percent of the effective cross-sectional area of said flow channel.

16. A forward scatter optical turbidimeter as recited in claim 9 whereinsaid signal processing means includes circuit means for electronicallyrejecting spurious signal excursions caused by bubbles in the flowingliquid.

17. A forward scatter optical turbidimeter as recited in claim 9 inwhich said light beam is made as thin in the direction of flow of theflowing liquid as is compatible with the sensitivity of said lightdetector means to provide a readable output signal.

18. A forward scatter optical turbidimeter as recited in claim 9 havinga pair of side walls parallel to said optical axis and in which saidlight beam is made as wide in the direction transverse to the flowingliquid as is compatible with the transverse width of the flow channelwithout coming in contact with said side walls.

19. A forward scatter optical turbidimeter as recited in claim 9 inwhich the height of said light beam in the direction of fluid is lessthan one-half of the width of said light beam in the directiontransverse to fluid flow.

1. A forward scatter optical turbidimeter comprising: a chamber forcontaining a liquid fluid sample the turbidity of which is to beevaluated, said chamber having opposite wall portions which areradiation transparent; means for defining a radiation axis through saidtransparent wall portions; source means disposed on one side of saidchamber for developing a beam of radiation and for directing said beamof radiation across said chamber through said wall portions along saidradiation axis; first radiation detector means disposed along saidradiation axis on the other side of said chamber for receiving said beamof radiation and for generating a first output signal commensurate withthe intensity of said beam of radiation after transmission through saidfluid sample; second radiation detector means disposed along saidradiation axis on the side of said first detector means opposite saidchamber; spatial radiation filtering means disposed between said firstand second detector means, said spatial radiation filter means beingarranged and dimensioned to project only the radiation scattered in theforward direction from a predetermined longitudinal segment of said beamof radiation which lies wholly within said chamber and is spacedinwardly from said wall portions onto said second detector means, saidsecond detector means generating a second output signal commensuratewith the intensity of the received forward scattered radiation; andsignal processing means responsive to said first and second outputsignals and operative to provide an indication of the turbidity of saidsample.
 1. A forward scatter optical turbidimeter comprising: a chamberfor containing a liquid fluid sample the turbidity of which is to beevaluated, said chamber having opposite wall portions which areradiation transparent; means for defining a radiation axis through saidtransparent wall portions; source means disposed on one side of saidchamber for developing a beam of radiation and for directing said beamof radiation across said chamber through said wall portions along saidradiation axis; first radiation detector means disposed along saidradiation axis on the other side of said chamber for receiving said beamof radiation and for generating a first output signal commensurate withthe intensity of said beam of radiation after transmission through saidfluid sample; second radiation detector means disposed along saidradiation axis on the side of said first detector means opposite saidchamber; spatial radiation filtering means disposed between said firstand second detector means, said spatial radiation filter means beingarranged and dimensioned to project only the radiation scattered in theforward direction from a predetermined longitudinal segment of said beamof radiation which lies wholly within said chamber and is spacedinwardly from said wall portions onto said second detector means, saidsecond detector means generating a second output signal commensuratewith the intensity of the received forward scattered radiation; andsignal processing means responsive to said first and second outputsignals and operative to provide an indication of the turbidity of saidsample.
 2. A forward scatter optical turbidimeter as recited in claim 1wherein said source means includes beam shaping means for shaping saidbeam of radiation into a flat ribbon which is substantially uniformalong its length.
 3. A forward scatter optical turbidimeter as recitedin claim 2 wherein said beam of radiation has a thickness of less than 5millimeters along tHe flat portion of said ribbon.
 4. A forward scatteroptical turbidimeter as recited in claim 3 wherein said beam ofradiation has a transverse width sufficient to occupy at least 50% ofthe effective cross-sectional area of said chamber through which saidlight beam passes.
 5. A forward scatter optical turbidimeter as recitedin claim 1 and further including a calibration means for permitting apredetermined amount of light, in the form of a calibration beam, topass through said chamber and only onto said second detector means.
 6. Aforward scatter optical turbidimeter as recited in claim 1 in which saidspatial radiation filtering means includes, an imaging lens system forimaging the scattered radiation onto said second detector means, and alimiting means cooperating with said second detector means to restrictthe imaged radiation to an annulus whose inner and outer diameterscorrespond, respectively, to the near and far end portion of saidlongitudinal segment.
 7. A forward scatter optical turbidimeter asrecited in claim 6 in which said limiting means includes a central maskoverlying said second detector means for defining the inner diameter ofsaid annulus.
 8. A forward scatter optical turbidimeter as recited inclaim 6 in which the radiation sensitive portion of said second detectormeans extends to and defines said outer diameter of said annulus.
 9. Aforward scatter optical turbidimeter for monitoring the turbidity of aflowing liquid comprising: a flow channel through which the flowingliquid is passed, said flow channel having opposite wall portions whichare optically transparent; means for defining an optical axis throughsaid transparent wall portions transversing said flow channel; lightsource means disposed on one side of said flow channel for developingand projecting a light beam, having a ribbon-like, substantially uniformcross section along its length, along said optical axis; first lightdetector means disposed along said optical axis on the other side ofsaid flow channel for receiving the light from said light beam which isdirectly transmitted and for generating a first output signalcommensurate with the intensity such directly transmitted light; seconddetector means disposed along said optical axis on the side of saidfirst detector means opposite said flow channel for receiving the lightfrom said light beam which is scattered in the forward direction and forgenerating a second output signal commensurate with the intensity ofsuch forward scattered light; and signal processing means responsive tosaid first and second output signals and operative to provide anindication of the turbidity of said fluid.
 10. A forward scatter opticalturbidimeter as recited in claim 9 wherein said light source meanscomprises a laser and a beam expanding means for developing said lightbeam.
 11. A forward scatter optical turbidimeter is recited in claim 9which further includes spatial optical filtering means disposed on theside of said first detector means opposite said flow channel portion,said filtering means being operative to project only the light scatteredin the forward direction from a predetermined longitudinal segment ofsaid light beam which lies wholly within said flow channel portion andwhich is spaced inwardly from said walls onto said second detectormeans.
 12. A forward scatter optical turbidimeter as recited in claim 11wherein said spatial optical filtering means includes, an imaging lenssystem for imaging the scattered radiation on said second detectormeans, and means to limit the area of sensitivity of said seconddetector means to an annulus whose inner and outer diameters correspondto the desired end portions of said longitudinal segments.
 13. A forwardscatter optical turbidimeter as recited in claim 9 which furtherincludes a calibration means for permitting a predetermined amount oflight, in the form of a calibration beam, to pass through said flowchannel and oNly onto said second detector means.
 14. A forward scatteroptical turbidimeter as recited in claim 9 wherein the transverse crosssection of said light beam is substantially rectangular and has athickness in the direction of the flowing liquid which is less then 5millimeters.
 15. A forward scatter optical turbidimeter as recited inclaim 9 wherein the width of said light beam is sufficient to occupy atleast 50 percent of the effective cross-sectional area of said flowchannel.
 16. A forward scatter optical turbidimeter as recited in claim9 wherein said signal processing means includes circuit means forelectronically rejecting spurious signal excursions caused by bubbles inthe flowing liquid.
 17. A forward scatter optical turbidimeter asrecited in claim 9 in which said light beam is made as thin in thedirection of flow of the flowing liquid as is compatible with thesensitivity of said light detector means to provide a readable outputsignal.
 18. A forward scatter optical turbidimeter as recited in claim 9having a pair of side walls parallel to said optical axis and in whichsaid light beam is made as wide in the direction transverse to theflowing liquid as is compatible with the transverse width of the flowchannel without coming in contact with said side walls.